Forcing circuit for inductors

ABSTRACT

For developing forcing current in a circuit in which prompt electrical response in inductive loads is desirable, a plurality of capacitances are charged in parallel at the working voltage of the source. When forcing voltage is required, the capacitances are disconnected from their parallel charging lines and connected in series for forcing purposes to supply the resulting high voltage into the circuit which exhibits the inductive property of opposing change in current. When two such circuits are to be forced in alternation, means is provided for dissipating the energy in one circuit concurrently with delivery of forcing voltage into the other. Versatility is enhanced by connecting the respective coils to separate sockets into which various capacitances, potentiometers and/or suppression units are interchangeably plugged.

United States Patent [72] Inventor Leo L. Stuckens Milwaukee, Wis.

[21] Appl. No. 835,408

[22] Filed June 23, I969 [45] Patented June 1, 1971 [73] AssigneeStearns Electric Corporation Milwaukee, Wis.

[54] FORCING CIRCUIT FOR INDUCTORS Primary Examiner-Robert K. SchaeferAssistant Examiner-William J. Smith Attorney-Wheeler, Wheeler, House andClemency ABSTRACT: For developing forcing current in a circuit in whichprompt electrical response in inductive loads is desirable, a pluralityof capacitances are charged in parallel at the working voltage of thesource. When forcing voltage is required, the capacitances aredisconnected from their parallel charging lines and connected in seriesfor forcing purposes to supply the resulting high voltage into thecircuit which exhibits the inductive property of opposing change incurrent. When two such circuits are to be forced in alternation, meansis provided for-dissipating the energy in one circuit concurrently withdelivery of forcing voltage into the other. Versatility is enhanced byconnecting the respective coils to separate sockets into which variouscapacitances, potentiometers and/or suppression units areinterchangeably plugged.

FORCING CIRCUIT FOR INDUCTORS BACKGROUND OF INVENTION The need forforcing circuits has long been recognized but heretofore such need hasbeen satisfied by charging the forcing capacitance to high voltage froma source which is separate from the source which supplies the workingcurrent. An example is U.S. Pat. 3,379,292 ofApr. 23, 1968.

SUMMARY OF INVENTION The present invention has many advantages. A majorfactor is the use of a single current source which supplies the workingcurrent while the circuit is in use, and at the same time, and with thesame voltage, charges forcing capacitances. In the device selected toexemplify the invention, there are clutch and brake actuating windingswhich are energized alternately and which desirably are immediatelyeffective when energized. The forcing circuit substantially eliminatesdelay which would otherwise be attributable to inductance. A singlesource supplies the windings in first and second circuits alternatelywith their working current while in use and at the same time charges inparallel a plurality of capacitances in one circuit. In practice, thereis a pair of capacitances serving each winding. When switching is doneto energize the brake and render the clutch inactive, or vice versa, thecoil which is deenergized has its energy dissipated and, at the sametime, the capacitances which were charged in parallel are connected inseries with the winding of the other circuit, thereby providing therequired forcing voltage.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a general schematic drawing of acircuit exemplifying the invention.

FIG. 2 is a diagrammatic plan view of a preferred mechanicalorganization of the components of the above circuit permitting parts tobe interchanged readily as desired.

DETAILED DESCRIPTION Particulars of the components are given hereafteronly by way of example and not by way of limitation.

Terminals 2 and 4 of a conventional l 15 volts 60 cycle circuit arerespectively connected to the terminals 6 and 8 of rectifier 10,preferably of a bridge type. In addition, a transientvoltage-suppressing device 12, comprising diodes back to back insymmetrical arrangement, is connected across the line. It protects therectifying bridge 10 against high voltage spikes. Connected between thepositive output terminal 14 and the negative output terminal 16 of thebridge 10 is a relay 18 controlled by switch 20. This relay mechanismmay be single or multiple. If there is a single relay, it would normallybe a four-pole double-throw device. Alternatively, it may consist of twoinstruments in parallel, each being doublepole double-throw.

The positive terminal 14 of the rectifier is connected by lead 22 to apair of diodes 24 and 26 which pass current only in a direction awayfrom the bridge circuit terminal.

The relay 18 includes a normally closed switch 28 which is a part of therelay as indicated by the broken line 30. Also included as a part ofrelay 18 is a normally open switch 32, its connection with the relaycoil being indicated by the broken line 34. Further included in therelay organization are the normally open switch 36 and the normallyclosed switch 38, relay actuation being indicated by the broken lines 40and 42 respectively. The four switches 28, 32, 36 and 38 are all in thecircuit switch controls of the winding 46. In the selected exarnple,this winding is the winding of an electromagnetically operated clutch.-

Included in the clutch winding controls are circuits of the capacitances50 and 52 which, when the switches 28 and 38 are closed, are charged inparallel through the resistor 54 and through the diodes 56 and 58,return connection being made via lead 60 and switch 38 to the negativeterminal 16 of the bridge rectifier 10.

For one particular installation, the resistor 54 is rated at 250 ohmsand 50 Watts in order to give the desired time constant of the resistorand capacitance assembly. In this assembly, the capacitors 50 and 52 areat 250 mfd. When connected in circuit, they are in parallel with eachother and in series with a resistor 54.

The same considerations apply to the resistor and capacitors 68 and 70.

However, for other installations, perhaps providing a more powerfulforcing circuit or involving other variables, the values would bemodified. Those given are merely by way of example of a particularinstallation.

When current is first supplied to the terminals 2 and 4, the firstcircuit and its capacitors 50 and 52, then connected in parallel, bothreceive current from the rectifier source 10. Concurrently, the coil 67in the second circuit is energized but without forcing current, sinceits capacitors 68 and 70 will not be charged until the switch 20 hasbeen closed.

The closing of switch 20 energizes relay 18 and supplies forcing currentfrom capacitors 50 and 52, then connected in series, to the clutchwinding 46. At the same time, the circuit completed by the closing ofnormally open switch 84 charges capacitances 68 and 70, then being inparallel and disconnected from brake coil 67.

The brake coil 67 will have dissipated its energy. It has beendisconnected from the supply circuit by the opening of normally closedswitch 65. Dissipation of its energy is assisted by the varistor 86. Inpractice, this varistor is a General Electric rod type THYRITEone-fourth inch in diameter (their number 6611-2100). A varistor hasresistance which varies according to voltage. It begins to conduct atabout 150 volts and its conductance increases exponentially withvoltage. As shown, the resistor 88 (10 ohms; 1 Watt) is connected acrossvaristor 86 in series with capacitance 90 (0.22 mfd. 600 V; DC).

The opening of switch 20 as shown in FIG. 1 deenergizes relay 18. Thevarious switches controlled by the relay assume the positionsillustrated in the drawing. The capacitances 50 and 52 previouslyconnected in series with each other and with clutch coil 46 in the firstcircuit are now connected in parallel with each other to receive currentfrom the rectifier l0. Capacitances 70 and 68, on the other hand, arenow connected in the second circuit in series with each other and withthe brake coil 67. These will now supply high voltage forcing current tothe brake coil 67. Supply of normal current and forcing current occursthrough the normally closed switch 65, with return through lead 60.

It will be understood that the alternatively energized coils 46 and 67are designated only for exemplification purposes as a clutch coil and abrake coil, respectively. Whatever the purpose for which they are used,the arrangement is such that repetitive opening and closing of themaster switch 20 will altemately apply normal current and forcingcurrent to the coils 46 and 67 in turn. One opening and closing sequenceof the switch is required before both of the forcing circuitcapacitances have been charged in readiness for connection in series tosupply forcing voltage to the respective circuit.

It is very important to note that the functioning of the apparatus asdescribed is dependent on the fact that alternate discharge paths fromthe capacitances are blocked by diodes as shown. Thus, in the circuitwhich includes coil 46, the diodes 56 and 58 and 92 and 26 cooperatewith the functioning of the switches as described, to require thecurrent to flow in parallel to the capacitances when these are beingcharged and preclude current flow from the series connected capacitancesin any direction other than through the forced coil 46.

The primary function of diodes 24 and 26 is to prevent discharge ofseries-connected capacitors in a first circuit into the capacitors ofthe other circuit wen the latter are at low voltage. At the end of therelay contact transfer, i.e., when charged capacitors 50 and 52 areseries-connected, they must not be able to discharge into the relativelyuncharged capacitors 68 and 70. The diode 26 prevents this. Similarly,when capacitors 68 and 70 in the second circuit are charged andconnected in series, the diode 24 prevents discharge into the thenuncharged capacitors 50 and 52 in the first circuit.

A secondary function of diodes 24 and 26 is to protect the bridge 10,which is the source of current for the two circuits. The bridge might bedestroyed in the event that its peak reverse voltage rating is below thevoltage of the series charge of the forcing capacitors. The bridge wouldbe required to block this high voltage and might not have a ratingadequate for the purpose.

Similarly, diodes 24, 78 and 80 require movement of the rectifiedcurrent in the correct direction for charging capacitances 68 and 70when these are connected in parallel and preclude discharge of theseries-connected capacitors 68 and 70 in any direction except throughdiode 74 and coil 67.

The functions of diodes 74 and 92 is also very important. The output ofthe bridge rectifier has an average DC voltage and is actually only0.637 of its peak magnitude voltage. Thus if the design is such as toyield an average voltage of 100 volts, as contemplated by the foregoingdiscussion, then the peak voltage would run to 157 volts. The diodes 74and 92 function to hold the voltage applied to the load (46 or 67) to avalue such as to be within the design-rated voltage.

It will be apparent from the foregoing description that each of the twocontrolled windings in which forcing is desirable during use has a setof capacitances which are charged in parallel from the same source whichenergizes the winding during use, and are discharged in series wheneverthe bridge circuit is connected to the respective windings for theenergization thereof. The initially high forcing current soondissipates, leaving the forced coil to be served with normal operatingvoltage from the rectifying bridge.

As suggested in FIG. 2, there are separate sockets 96 and 98 mounted ona carrier 100 and to which are connected through barrier block 99 therespective coils 46 and 67 shown in FIG. 1. The remaining components ofthe forcing circuits of FIG. I or, alternatively, conventional arcsuppression or potentiometer units may be plugged into these sockets inalternation with the forcing units above described.

For example, it may be desired to obtain a sharp response from one ofthe coils 46 or 67 and a soft response from the other. Alternatively, itmay be desired to substitute a potentiometer or an arc suppression unitor either or both for the forcing unit. This is readily possible in theFIG. 2 constmction since it is only necessary to replace a forcing unit102 with an arc suppression unit 104 or a potentiometer unit 106,according to the effect desired.

The plug-in forcing unit 102 may include the diodes 26, 92, 56 and 58(or 24, 74, 80 and 78); the capacitance 66 (or 90); the resistor 64 (or88) and the varistor 62 (or 86); and the capacitances 50 and 52 (or 68and 70).

The are suppression plug-in unit 104 contains the capacitance 66 (or90); the resistor 64 (or 88); and the varistor 62 (or 86).

The potentiometer and suppression unit 106 contains a potentiometer 108;and the capacitance 66 (or in series with the resistor 64 (or 88); thesebeing coupled across the varistor 62 (or 86).

lclaim:

1. In a circuit having inductance, forcing means comprising a pluralityof capacitances, a source of working voltage for said circuit, switchingmeans for connecting said source to the circuit and to the capacitancesin parallel, and switching means for selectively breaking the connectionin parallel and connecting said capacitances in series to said circuit,said circuit including a rectifier, a relay coil, a plurality ofelectromagnetic windings, means for dissipating energy from a winding,said switching means being controlled by the relay coil and includingmeans for alternately connecting energy dissipating means to respectivewindings, there being a plurality of capacitances for each of saidelectromagnetic windings, said switching means including means forconnecting the source to the capacitances for one such winding and forconnectmg said last capacitances in parallel at a time when the energydissipating means is connected to another winding, and means forconnecting the capacitances in series to a respective winding which isconnected to said source and is disconnected from the energy dissipatingmeans.

2. A circuit comprising the combination with a clutch winding and abrake winding, of a rectifier, a relay including a coil and a controlswitch, a pair of capacitances for each said winding, current controlmeans for directing current from said rectifier in parallel through onepair of said capacitances, control means for directing current in seriesthrough the other pair of capacitances and through the other saidwinding, and means for interchanging the connections of saidcapacitances for directing current from said rectifier in parallelthrough the second set of capacitances while connecting the first set ofcapacitances in series with each other and with the first said winding.

3. A circuit according to claim 2 in further combination with means forselectively dissipating energy from the winding to which thecapacitances are not connected in series, and during the parallelconnection to the rectifier of the pair of capacitances for the lastmentioned winding.

4. The combination with a current source, of two circuits each having aninductance and each having forcing means comprising a plurality ofcapacitances, switching means for connecting said source and the saidcapacitances of one of said circuits in parallel and for connecting thecapacitances of the other of said circuits in series to the inductancethereof, said switching means including means for reversing theconnections to connect said source to the capacitances of said lastmentioned circuit in parallel and for connecting the capacitances of thefirst mentioned circuit in series to its respective inductance, saidswitching means further including diodes for isolatingparallel-connected capacitances from the voltage of series-connectedcapacitances.

1. In a circuit having inductance, forcing means comprising a pluralityof capacitances, a source of working voltage for said circuit, switchingmeans for connecting said source to the circuit and to the capacitancesin parallel, and switching means for selectively breaking the connectionin parallel and connecting said capacitances in series to said circuit,said circuit including a rectifier, a relay coil, a plurality ofelectromagnetic windings, means for dissipating energy from a winding,said switching means being controlled by the relay coil and includingmeans for alternately connecting energy dissipating means to respectivewindings, there being a plurality of capacitances for each of saidelectromagnetic windings, said switching means including means forconnecting the source to the capacitances for one such winding and forconnecting said last capacitances in parallel at a time when the energydissipating means is connected to another winding, and means forconnecting the capacitances in series to a respective winding which isconnected to said source and is disconnected from the energy dissipatingmeans.
 2. A circuit comprising the combination with a clutch winding anda brake winding, of a rectifier, a relay including a coil and a controlswitch, a pair of capacitances for each said winding, current controlmeans for directing current from said rectifier in parallel through onepair of said capacitances, control means for directing current in seriesthrough the other pair of capacitances and through the other saidwinding, and means for interchanging the connections of saidcapacitances for directing current from said rectifier in parallelthrough the second set of capacitances while connecting the first set ofcapacitances in series with each other and with the first said winding.3. A circuit according to claim 2 in further combination with means forselectively dissipating energy from the winding to which thecapacitances are not connected in series, and during the parallelconnection to the rectifier of the pair of capacitances for the lastmentioned winding.
 4. The combination with a current source, of twocircuits each having an inductance and each having forcing meanscomprising a plurality of capacitances, switching means for connectingsaid source and the said capacitances of one of said circuits inparallel and for connecting the capacitances of the other of saidcircuits in series to the inductance thereof, said switching meansincluding means for reversing the connections to connect said source tothe capacitances of said last mentioned circuit in parallel and forconnecting the capacitances of the first mentioned circuit in series toits respective inductance, said switching means further including diodesfor isolating parallel-connected capacitances from the voltage ofseries-connected capacitances.